Chromebook Enable Developer Mode

https://www.quora.com/How-do-I-dual-boot-Linux-on-a-Chromebook
Step One: Enable Developer Mode


This will wipe your local data, so make sure to back anything up that you don't have stored in the cloud. To put your Chromebook in Developer Mode:

Press and hold the Esc and Refresh keys together, then press the Power button (while still holding the other two keys). This will reboot your Chromebook into Recovery Mode.
As soon as you see Recovery Mode pop up -- the screen with the yellow exclamation point -- press Ctrl+D. This will bring up a prompt asking if you want to turn on Developer Mode.
Press Enter to continue, then give it some time. It'll pop up with a new screen for a few moments, then reboot and go through the process of enabling Developer Mode. This may take a little while (about 15 minutes or so), and will wipe your local information.
When it's done, it will return to the screen with the red exclamation point. Leave it alone until it reboots into Chrome OS.
Note that some older Chromebooks have a physical switch that you'll have to flip in order to turn on Developer Mode. If you aren't sure, look up instructions for your specific device on enabling Developer Mode.